Signaling system



June 20, 1944- H. E. VAUGHAN SIGNALING SYSTEM.

Filed Jun`e 29, 1943 2 Sheets-Sheet 1 n /NVENTO H E. VAI/@HAN d Q Arron/ver June 20, 1944.

H. E. VAUGHAN `SIGNALINGr SYSTEM Filed June 29, 1943 2 sheets-sheet'z Se; n

By @M ATToR/VEV Patented June 20, 1944 UNITED STATES PA' r'wlazllvTf "or-Fics SIGNALING Henry E. Vaughan, Valley Stream, N. Y., assigner 5 V to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 29, 1943, Serial No. 492,675

12 claims. (0 1. 17e-175.2)

This invention relates to selective switching systems and particularly to signal repeating and key monitoring in automatic telephone systems.

Objects of the invention are the provision of new and improved signal receiving means in automatic telephone systems and the provision of a key monitoring circuit arrangement which does not interfere with the transmission of key-set signals. Another object is an increasev in the length of line over which key-set signals may be satisfactorily transmitted.

One feature of the invention is a key monitoring apparatus comprising means adapted to repeat key-set signal impulses, the arrangement having a high impedance so as not to interfere with the transmission of the signals and establishment of desired connections. Another feature of the invention is a signal receiving circuit arrangement comprising vacuum tubes and relays responsive to polarized and marginal key-set signal impulses transmitted over each of the two conductors of a trunk line.

A clear and complete understanding of these and other features of the invention will be facilitated by a description of a system in which the invention is embodied, one such system being represented schematically in the drawings which form a part of this specification. The invention is not limited in its application to the system shown in the drawings but is generally applicable to any signaling system arranged to transmit polarized and marginal signal impulses.

Referring to the drawings:

Fig. 1 shows an operators position comprising a cord vCD and a key-set KS, an outgoing trunk j circuit OTI, link LK, register sender RS, incoming selector switch IS, connector switch CS, and a called subscribers line and station B; and 1 Fig. 2 shows a key monitoring circuit KM comprising means for registering and indicating the digits transmitted by the operation of the key-set KS of Fig. 1.

The operators position comprising the cord CD and key-set KS may be one of a plurality of similarly equipped positions of a dial system A switchboard or of a toll or other manual office. Reference may be had to Patent No. 1,916,760, granted to I. H. Henry, July 4, 1933, for a complete dis'- closure of an operators cord, position and keyset circuits. The outgoing trunk circuit OTI, link had to the 2nd edition of --Automatic telephony by'Smith and Campbell, pages 53 to 65 for a description of such switches and their operation when used as selectors and connectors.

The key monitoringl circuit KM, which` is similar -to that disclosed in Patent No. 1,753,348, granted to J. B. Newsom, April 8,1930, comprises two' vacuum tubeunits 2|0 and 230 which are connected respectively to the ltip and ring conductors of the key-set KS in parallel with the register relays of a register sender by a relayl I5 which is operated-responsive to the insertion' of a plugI H3 in the monitoring -jackflllL .They key monitoring circuit KM further comprises sets of digit register relays and lamps for registering and indicating the digits which are being transmitted to the register sender by operation of thekey-set KS, only one of these sets of register relays and lamps being shown. The key monitoring circuit KM'further comprises relays 253, 255 and 251 which are controlled by vacuum tube unit 2|0 and relays 254, 256 and 258 which are controlled by vacuum tube unit 230 for operating the sets of register relays. These relays, 253 to 258 inclusive, are similar to relays |33 to |38, inclusive, ofithe register sender RS. Each of relays |33, |34, 253 and 254 is a polarized relay which is operated only. responsive to the connection of .4S-.volt .battery to the associated one of conductors |3I, |32, 25| and 252. Each ofrelays |35, |36, 255 and 256 isa marginal relay which is operated only when ground or48-volt battery is connected through a low resistance to the associated one of conductors |3|, |32, 25| and 252. Each of relays |31, |38, 251 and 258 is a sensitive, non-polarized'relay which is `operatively energized whenever either ground or L8-volt battery is connected to the associated one of conductors |3|, |32, 25| and 252. The unit 2|0 comprises two, stabilized, negative-feedback, direct-current amplifiers 2 5 and 225, one for distinguishing between positive and negative signals and the other for distinguishing between the connection. of ground or battery to' conductor 20| through a low resistance and the connection of yground or battery to conductor 20| through a high resistance. The control grids of tubes 2|5 and 225 are connected to conductor 20| through a resistor 2| l'and are shunted by a condenser 2|3, this arrangement being effective to minimize the effects of transients produced by operation of the keys of key-set KS. The connection between the control grid vof tube 225and conductor 20| includes resistor 22| in .series with resistor 2| l. The repeater unit 2|0 further comprises -two p0- rlarized relays 2|6 and 2|'| controlled by tube 2|5 and a relay 226 controlled by tube 225. Each of relays 2|6 and 2I1 has two windings, the upper winding being connected in series with the plate of tube 2|5. The energization of the lower windings of relays 2 I 6 and 2 I 1 is constant in value and opposes the energization of the upper windings. When the Ll8-volt battery |00 is connected by the operation of a key vof key-set KS to conductor III, the grid of tube 2I5 becomes more negative with respect to the cathode and the plate current decreases sumciently to eiect the operation of relay 2|6; and when ground potential is applied by the operation of a key of key-set KS to conductor III, the grid of tube 2|5 becomes more positive with respect to the cathode and the plate current increases sufciently to effect the operation of relay 2I1. The resistor 2I4 connected in series with the cathode provides the desired grid bias and negative feedback and provides compensation for variation in the battery voltage. Relay 226 is a differential relay the lower winding being connected in series with the plate of tube 225. The energization of the upper winding of relay 226 is-neutralized bythe` energization of the lower winding of relay 226 by the normally existing currentV in the plate circuit of tube 225; but when the plate circuit is either increased or decreased responsive to the operation of a key of key-set KS, relay 226 operates. Relays 2I6, 2I1 and 226 are thus controlled by tubes 2 I 5 and 225 to repeat to relays 253, 2,55 and 251 the key-set impulses which are transmitted over conductor II I to relays I33, I35 and |31 of the register sender.

Transients over conductor `20| are largely due to the inductance of the windings of the impulse receiving relays yconnected to conductor III in the attached register sender. At the instant a key-set key is operated to transmit an impulse vover conductor III, the windings of these relays constitute a very high impedance and there is only a small voltage drop through the resistors at the key-set. Thus the voltage impressed on 'conductor 20|, at the beginning of a key-set impulse over conductor III, is substantially equal to the full battery voltage. The condenser 2I3 constitutes a low impedance at the beginning of van impulse and therefore the drop in voltage .across resistor 2|| is nearly equal to the battery voltage. Condenser 2I3 absorbs this transient voltage and also absorbs the reverse voltage generated in the windings of the impulse receiving relaysy connected to conductor III when the depressed key-setkey is restored to normal. Without resistor 2II and condenser 2I3, it would be impossible to distinguish between high and low resistance impulses transmitted over conductor III and false operations of the key monitoring register relaysr would also result from the opposite voltage generated in the windings of the impulse receiving relays of the register sender at the end of a key-set impulse.

The repeater unit 230 is similar to the unit 2I0 and is effective to repeat to relays 254, 256 and 258 the key-set impulses which are transmitted over conductor II2 to relays |34, |36 and |38 of the register sender.

Assume now that the plug II3 has beenV inserted in monitoring jack I|4,. operating relays II5 and 200. The operation of relay I|5 connects conductors III and II2 to conductors. 20| and 202 to transmit key-set impulses to the monitoring circuit KM at the same time that these impulses are transmitted to an associated register sender to control the establishment of a desired connection. The connection of the key-set KS to the key monitoring circuit KM and operation of relay 206 prepares the monitoring circuit for response to key-set impulses, relay 266 being operated to connect the rst set of register relays 266 to the contacts of relays 253', 254, 255 and 256 in similar manner to that in which the first set of register relays are connected to the impulse responsive relays in the aforementioned patent to Newsom.

When an operator inserts the calling plug CP of a cord CD in jack JI of an outgoing trunk circuit OTI, a register sender RS is associated .with the trunk circuit in the manner set forth in the aforementioned patent to Henry. U-pon operation of a position key, relay |20 is operated and the key-set KS is connected through the tip and ring conductors of plug CP and conductors I2| and |22 of outgoing trunk circuit OTI to conductors |3I and |32 of the register sender. When a register sender RS is ready to receive key-set impulses, a relay is operated and pilot lamp lighted at the operators position, to indicate that operation of the key-set may be initiated, and battery and ground are connected to the key-set all as described in detail in the aforementioned Henry patent.

If the rst digit key operated, is the key 1, a circuit is closed from ground through low resistance |013, contacts of key 1, conductor III, tip conductor of plug CP and jack J I, conductors |2I and I3I, and windings of relays |33, I35 and |31 to 2lvolt battery; whereby relays I35 and |31 are operated but relay |33 is not operated. At the same time, the potential of the grid of tube 2| 5 becomes sufficiently more positive with 4respect to the cathode to effect the operation of relay 2'I1 and the potential of the grid of tube 225 becomes sufficiently more positive with respect to the cathode to effect the operation of relay 226. lWith relays 2'I1 and 226 operated, ground is connected to conductor 25| to effect the operation of relays 255 and 251 without operating relay 253. The operation of relay 255 closes a circuit including a front contact of relay 266 vfor operatively energizing the right winding Vof-relay 26|. Relay 26| locks through its left winding and prepares a circuit for energizing the lamp 1 of lamps 210. When the key 1 is released, relays 2I1 and 226 release, causing the release of relays 255 and 251 but relay 26| remainsv operated. The operation and release of relay 251 effects the release of relay 266 and the connection of the contacts of relays 253, 254, 255

and 256 to the next set of register relays in the manner set forth in detail in the aforementioned patents'to Henry and Newsom.

If the rst digit key which is operated is the key 2, a circuit is closed Vfrom 48-volt battery through low resistance IDI, high resistance |62, contacts of key 2, and conductor I I I` for operating relays |33 and |31 in the register sender. At the same time, the potential of the grid of tube 2|5 becomes sufficiently negative with respect to the cathode to effect the operation of relay 2|6; but the potential oi the grid of tube 225 does not become sufliciently negative with respect to the cathode to effect the operation of relay 226. With relay 2I6 operated and relay V226 non-operated, L8-volt battery is connected through resistor 221 to conductor 25| to effect the operation of relays 253 land 251 without operating relay 255. The operation of relay 253 closes a. circuit for operatively energizing the vright winding of relay 262.- `Relay 262 locks through its'left windin'gfandl prepares a` circuit forlightinglamp 2 of lamps 210.A f

If the r's't .digit-key Which is operated is the key` 3, a circuit isclosed Yfrom LlS---volt battery throughlow'resistance |0|, and the contacts of key 3 for operating relays |33, |35 and |31 of the register sender; and at the same time the potential of the .grids of tubes 2|5 and 225 is changed suiciently to. eect Vthe operation of relays 2|6 and 226. .With relays 2|5 and 226 operated, 48-volt battery isconnected directly to conductor 25|, causing the operation of. all .of relays 253, 255 'and 251. The right windings of both of relays v2|5l'and 262 are thereby operatively energized and these relays lock through their left windings and prepare a circuit for lighting lampB.

If the rst digit key which is operated is the key 4,. a-circuit is closed from ground through low resistance |04, high resistance |03, right contact of key 4 and conductor for operating relay |31 in the register sender without operating relays |33 and |35; and a circuit is closed from battery |00 through low resistance |0|, high resistance |02,vleft contactvof'key 4.- and conductor ||2 for operating relays |34 and |38 in the register sender without operating relay |36. At the same time, the change in the potential of the grid of tube 2|5 with respect to the cathode elfects the operation ofv relay 2|1 but the change in thel potential of the grid of tube 225 is ineffective to cause the operation of relay 225; and the change in the potential of the grid of tube 235 -With respect to the cathode effects the. operation of relay-236, but the charge in the potential of the grid of tube `245 with respect to the cathode is ineffective to cause the operation of relay 246; 4The operation of relay 2|1 closes a circuit through resistor 221 for operating relay 251 Without operating relays'253 and 255 and the operation of relay 236 closes a circuit through resistor 241 for operating relays 254 and 25B Without operating relay`256. The operation of relay 254 closes a circuit for operatively energizing the left winding ofrelay '264.l Relay 264 locks through its right Winding and prepares a circuit for lighting lamp 4.

If the first digit keywhich is operated is the key 5, a circuit is closed from ground through low resistance |04, high resistance |03, right contact ofkey 5, and conductor for operating relay |31 in the register sender without operating relays |33 and |35; and. a circuit is closed from ground through W resistance |05, left contact of key 5, and conductor ||2 for operating relays |36and l|38 in the register senderwithout operating relay |34. At the same time, the change in the potential of the grid of tube 2|5'W'ith respect' to the cathodeeffects the operation of relay 2|1 lbut the change in the potential of the grid of tube 225 with respect to the cathode is ineiective to cause the Operation of relay 226; and the change in thepotential ofthe grid of tube 235 with respect to the cathode is eiective to cause the operation of relay I231 and the change in potential ofthe grid of tube245 with respect to theacathode is effective to cause the operation of relay 246. The operation of relay 2|1 causes the operation of relay 251 Without operating relays 253 and 255 and the operation of relays 231 and 246 causes the operation of relays 256 and 258v Without operating relay 254. vThe operation'of relay 256 closes a circuit for operatively nergigingthe left IWinding of relay 265. Relay265 'locks through itsjright Winding, and prepares '.a'circuit for lighting lamp A5.

If the rst digit key which is operatedis theI key `6, a circuit is closedffromA 1ground through 10W resistance |04,v right contact of key 6v and conductor for operatingrelays ,|35 and |31 in the register sender Without operating relay-l 33;I and a circuit is closed fromvground throughlowv resistance` |05, left contact of key 6, and con, ductor ||2 for operating relays .|36 vand |38-jin theregister sender without operating relay |34. At the sare time, the changehin potential of the grid of tube 2|5Withrespect to the cathode effects Athe operation of relay 2|1;';the chan-ge in potential of the grid lof ,tube 225` with respect to the cathode effects the operation of,r relay 226;, the change inthe po-tentialof the grid of tube 235 with respect to the cathode eiectsthe op. eration of relay 231; and the `change in the potential of the grid of'tube l245 with respect to the cathode eiects the operation of relay 245. 'Ihe operation of relays 2|1 and 2.26 closes L a Vcir cuit. for operating relays 255 and 251 Without operating relay 253; andthe operation of relays 231 and 256 closes a circuit for'operatingA relays 256 and 2523k without operating relay/254. The operation of relay 255 closes a circuit for operatively energizing the right winding, of relay 2511;'l and the operationof relay 256 closes a circuit' for operativelyenergizing the left Winding'of relay 255. .Relays 26| and 265 close locking cir,-4 cuits and prepare a circuit for lighting lanipj. If the rstdi-git key Which is operated is the key '1, a circuit is closed from battery |00 through low. resistance |01, high resistance |02, right contact of key 7 and. conductor for loperating' relays V|33 and |31 `in the register sender without operating relay |35; and a circuit is closedfrorn ground through` low resistance |05', leftcontact of key 7 and' conductor 2 for operatingrelays 36 and |38 vin the register sender Without operat: ing relay' |34. At the same time, the change'in the potential of the grid of 'tube 2|5.with 'respect to the .cathode effects the operation of frelay' 2|6 but the change in the potential of the grid of tube 225 with respect to thefcathode is ineffective to cause the operation of' relay 226;Y andthe change in the potential ofthegridof tube 235 with respect to the cathodeeffectsthe operation of relayA 231. IWhile the change in the potential of the -grid of tube 245 with respect toj the cathode effects the operation 'of relay` 2461. The operation of relay'2l6 vcloses a circuit for operating relays 253 and 251 without operating relay 255; and the operation of relays 2,3`|"a`nd 246 closes a circuit foroperating relays" 256 and 258' Without operating relay l251|. The operation of relay 253 closes a circuit for operatively energizing the right'vvinding of`relay 262v V'and lthe operationv of relay 255 closes a -circuit for ope' eratively energizing the left `Winding of relay2'65. Relays 262 and 265 lock and prepare a circuit Vfor lighting lamp '1. If the rst digit key which is operated isv the key 8, a circuit is closed frombattery |00 through low resistance I0 rightcontact of key 8 and 'con` ductor for operating relays |33', |35`and |31 in the' register sender anda circuit is closed from ground through low'r'esistancejlllS, leftcontact of key 8 vand* conductor |2 for operating relays |36 and |'38` in the register sender Without Oper ating relay |34. At the same time, therefis, a change in the potential/of the grid of tube 2|5 with respect to the cathode which causes.thepperation ofvrelay12|5and a'. change in=the poten` tial of the grid ofV tube 225 with respect to the cathode which causes the operation of relay 226; and there is a change in the potential of the grid of tube 235 with respect to the cathode which causes the operation of relay 231 and a change in the potential of the grid of tube 245 with respect to the cathode which causes the operation of relay 246. The operation of relays 2|6 and 226 closes a circuit for operating relays 253, 255 and 251; and the operation of relays 231V and 246 causes the operation of relays 256 and 258 without operating relay 254. The operation of relays 253 and 255 closes circuits for operatively energizing the right windings of relays 26| and 262 and the operation of relay 256 closes a circuit for operatively energizing the left winding of relay 265. Relays 26|, 262'and 265 lock and prepare a circuit for lighting lamp 8.

If the first digit key which` is operated is the key 9, a circuit is closed from ground through low resistance |04, high resistance |03, right contact of key 9 and conductor for operating relay |31 in the register sender without operating relays I33 and |35; and a circuit is closed from battery through low resistance |0|, left contact of key 9 and conductor ||2 for operating relays |34, |36 and |38 in the register sender. At the same time, the potential of the grid of tube 2|5 is changed with respectto the cathode to effect the operation of relay 2|1, but the change in the potential of the grid of tube 225 with respect to the cathode is ineffective to cause the operation of relay 226; and the change in potential of the grid of tube 235 with respect to the cathode effects the operation of relay 236 while the change in potential of the grid of tube 245 with respect to the cathode causes the operation of relay 246. The operation of relay 2 1 closes a circuit through resistor 221 for operating relay 251 without operating relays 253 and 255; and the operation of relays236 and 246 closes a circuit for operating relays 254, 256 and 258. The operation of relays 254 and 256 closes circuits for operatively energizing the left windings of relays 264 and 265. Relays 264 and 265 lock and prepare a circuit for lighting lamp 9.

If the first digit key which is operated is the key 0, a circuit is closed from ground through low resistance |04, high resistance |03, contacts of key 0 and conductor for operating relay |31 in the register sender without operating relays |33 and |35. At the same time, the potential of the grid of tube 2|5 is changed with respect to the cathode to eiect the operation of relay 2|1 but the change in the potential of the grid of tube 225 with respect to the cathode is ineffective to cause the operation of relay 226. The operation of relay 2|1 closes a circuit through resistor 221 for operating relay 251 .without operating relays 253 and 255. Since none of relays 253, 255, 254 and 256 are operated responsive to the depression of key 0, none of register relays 26|, 262, 264 and 265 is operated and the normally prepared circuit for lighting lamp -0 is pletes the circuits for lighting the digit indicating lamps which correspond to the digit keys which were depressed, thereby enabling a monitoring operator to check the number actually keyed -with the number requested by a calling operator or subscriber- The key-set is disconnected after keying is completed and thedesired connection is established through switches IS and C under the control of the register sender in the manner set forth in the aforementioned Henry patent.

What is claimed is:

1. In combination, a thermionic valve, signaling means for selectively impressing negative and positive electromotive forces across the grid and cathode of said valve, a polarized relay having two windings, means energizing one of the windings in the anode-cathode circuit of said valve, and means energizing the other winding of said relay, the normal energization of said one winding being effective to neutralize the energization of said other winding, the change in the energization of'said one winding responsive to the application of an electromotive force of one polarity across the grid and cathode being ineffective to operate said relay and the change in the energization of said one winding responsive to the application of an electromotive force of opposite polarity across the grid and cathode being effective to operate said relay.

2. In combination, a thermionic valve, signaling means for selectively impressing negative electromotive forces of two different magnitudes and positive electromotive forces of two different magnitudes across the grid and cathode of said valve, a differential relay, means energizing one of the windings of said relay in the anodecathode circuit of said Valve, and means energizing the other winding of said relay, the normal energization of said one winding being effective to neutralize the energization of said other winding, the change in the energization of said one winding responsive to the application of an electromotive force of the lower of said two magnitudes of either polarity being ineffective to operate said relay and the change in the energization of said one Winding responsive to the application of an electromotive force of the higher of said two magnitudes of either polarity being effective to operate said relay.

3. In combination, a thermionic valve, signaling means for selectively impressingfnegative and positive electromotive forces across the grid and cathode of said valve, two polarized relays each having two windings, means energizing one winding of each of said relays in the anode-cathode circuit of said valve, means energizing the other winding of a nrst one of said relays, and means energizing the other winding of the second of said relays, the normal energization of said one winding of each of said relays being effective to neutralize the energization of said other winding, the change in the energization of said one winding of said first relay responsive to the application of an electromotive force o f one polarity across the grid and cathode of 'said valve being effective to operate said first relay and the change in the energization of said one winding of said second relay responsive to the application of an`electromoti`ve force of lopposite polarity across the grid and cathode of said valve being effective to operate said second relay.

4. In a signaling system, a conductor, ysignal receiving means connected to said conductor,'and means Afor selectively transmitting polarized di'- rect current signalsover said conductor, said signal receiving means comprising a thermionic polarized relay having two windings, means `energizing one of the windings, and means energizing the other winding in the'anode-cathode circuit of said valve', the normal energization of said other winding being effective to neutralize the energization of said one winding, the change in the energization of said other winding responsive to a direct current signal of one polarity being ineffective to cause the operation of said relay, and the change in the energization of said other winding responsive to a direct current signal of the opposite polarity being effective to cause the operation of Said relay.

5. In a signaling system, a conductor, signal receiving means connected to said conductor, and means for selectively transmitting marginal and polarized direct current signals through said conductor, said signal receiving means comprising a thermionic valve, a high impedance element connecting the control element of said valve to said conductor, a marginal differential relay having one winding energized in the anode-cathode circuit of said valve, and means energizing the other winding of said relay, the energization of said other winding lbeing effective to neutralize the normal energization of said one winding, thet change in the energization of said one winding responsive to the transmission of a direct current signal of either polarity through said conductor being ineffective to operate said relay Vin the case of a low amplitude signal current and,

effective to operate said relay in the case of a high amplitude signal current.

6. I n a signaling system, a conductor, signal receiving means connected to said conductor, and means for selectively transmitting polarized di- 1 rect current signals over said conductor, said signal receiving means comprising a thermionic valve, a high impedance element connecting the control element of said valve to said conductor, two polarized relays each having two windings, means energizing one winding of each of said relays in the anode-cathode circuit of said Valve, means energizing the other winding of one of said relays, and means energizing the otherfwinding of the other of said relays,'the normal energization of said one winding of each of said relays being eifective to neutralize the energization of said other winding, the change in the energization of said one winding of said one relay responsive to a direct current signal of one polarityt being effective to operate said one relay and the change in the energization of'said one winding of said other relay responsive to a direct current signal of opposite polarity being effective to operate said other relay.

'7. In a signaling system, a conductor, signal receiving means connected to said conductor, and means for selectively transmitting marginal and polarized direct current signals through said conductor to said signal receiving means, said signal receiving means comprising a rst thermionic valve, a second thermionic valve, a high impedance element connecting the control element of said first Valve to said conductor, two polarized relays, each having a biasing winding and an operating winding, means energizing said biasing windings, means energizing said operating windings in the anodecathode circuit of said rst valve to effect the operation of one of said relays responsive to a direct current signal of one polarity and to effect the operation of theother of said relays responsive to a direct current signal of the opposite polarity, another high impedance element connecting the control element of said second valve to said conductor in series with the first-mentioned high impedance element, a marginal differential relay having. one winding energized in the anode-cathode circuit of said second valve, and means energizing the other winding of said differential relay, the energization of saidv other Winding being effective to neutralize the normal energization ofv said one winding, the change in y ential relay and the change in the energization of said one winding responsive to the transmission of a high amplitude signal of either polarity through said conductor being effective to operate said differential relay.

8. A signal receiving circuit adapted to respond to polarized and marginal signals, said circuit comprising two vacuum tubes and three relays, means connecting the grid of one of said tubes to a conductor over which said signals'are transmitted to impress on said grid substantially the entire voltage derived from transmission of a signal, means connecting the anode of said one tube to windings of a rst and a second one of said relays to effect the operation of said r'st relay responsive to the impression of a positive voltage on said conductor and the operation of said second relay responsive to the impression of a negative voltage on said conductor, means connecting the grid of the other of said tubes to said conductor to impress thereon only a part of the voltage derived from transmission of a signal, and means connecting the anode of said other tube to the winding of the third of said relays to effect the operation of said third relay only in response to the impression of a substantially higher voltage of either polarity to said conductor than that which is effective to operate said rst or second relays.

9. In a signaling system, means adapted to repeat polarized and marginal signals, said means comprising two thermionic valves, means convnectingthe'grid of one of said valves to a conductor over which said signals are transmitted to impress on said grid substantially the entire voltage derived from'transmission of a signal, two polarized relays, means for biasing said relays, means for energizing a winding of each of saidrelays in the anode-cathode circuit of said Vone valve to effect the operation of one of said relays responsive to the transmission of a signal of one polarity and to effect the operation of the other of said relays responsive to the transmission of a'signal of the opposite polarity, means connecting the grid ofthe other of said valves to the conductor over which said signalsv are transmitted to impress 'on' said grid only a part of the voltage derived from the transmission of a signal, a differential relay having one winding energized in the anode-cathode circuit of said other valve, means energizing another winding of said differential relay to neutralizey the normal energization of said one winding, the change in the energization of said one winding of said differential relayresponsive to signals of maximum amplitude of either polarity being effective to oper-- ate said relay, the change in the energization of said one winding of said differential relay responsive to signals of less than maximum amplitude of either polarity being ineffective to operate said relay, signal relays, and means controlled rby saidfpolarized and differential relays for selectively operating said signal relays.

ing established over said conductors responsive to the operation of each of the digit keys, said signal receiving means comprisin-g a first thermionic valve, means connecting the grid of said first valve to one of the conductors of said line to impress on said grid the entire voltage derived from the closure of a signaling circuit over said v one conductor, a first polarized relay, a second polarized relay, means energizing one Winding of each of said first and second polarized relays in the anode-cathode circuit of said rst valve,

meansenergizing another winding of each 0f said yfirst and second polarized relays, the normal energization of said one Winding of each of said first and second polarized relays being effective to neutralize the energization of said other winding, the change in the current in the anode-cathode circuit of said first valve responsive to the closure of a signaling circuit over said one conductor from a source of electromotive force of one polarity being effective to operate said first polarized relay and the change in the current in the anode-cathode circuit of said first valve responsive to the closure of a signaling circuit over said one conductor from a source of electromotive force of the opposite polarity being effective to operate said second polarized relay, a second,

thermionic valve, means connecting the grid of said second valve t0 said one of the conductors of said line to impress on said grid only part of the voltage derived from the closure of a signaling circuit over said one conductor, a first differential relay, means energizing one Winding of said first differential relay in the anode-cathode circuit of said second valve, means energizing another Winding of said first differential relay, the normal energization of said one Winding of said first differential relay being effective to neutralize the energization of said other winding, the change in the energization of said one Winding of said first differential relay responsive to the closure of a high resistance signaling circuit over said one conductor from either of said sources of electromotive force being ineffective to operate said first differential relay and the change in the energization of said one Winding of said first differential relay responsive to the closure of a low resistance signaling circuit over said one conductorfrom either one of said sources of electromotive force being effective to operate said first differential relay, a third thermionic valve, means connecting the grid of said third valve to the other conductor of said line to impress on said grid the entire voltage derived from closure of a signaling circuit over said other conductor, a

third polarized relay, a fourth polarized relay,

means energizing" one `Winding of each of said third and fourthjpolarized relays in the anodecathode circuit of ysaid third valve, means energizing another Winding of each of said third and fourth polarized relays, the normal energization of said one Winding of each of said third and fourth polarized relays being effective to neutralize the energization of said other Winding, the change in the current in the anode-cathode circuit of said third valve responsive to the closure of a signaling circuit over said other conductor from a source of electromotive force of one polarity being effective to operate said third polarized relay and the change in the current in the anode-cathode circuit of said third valve responsive to the closure of a signaling circuit over said other conductor from a source of electromotive force of the opposite polarity being effective to operate said fourth polarized relay, a fourth thermionic "valve, means connecting the grid of said fourth valve to said other conductor to impress on said grid only a part of the voltage derived from closure of a signaling circuit over said other conductor, a second differential relay, means energizing one Winding of said second differential relay in the anode-cathode circuit of said fourth valve, and means energizing another Winding of said second differential relay, the normal energization of said one Winding of said second differential relay being effective to neutralize the energization of said other Winding, the change in the energization of said one winding of said second differential relay responsive to the closure of a high resistance signaling circuit over said other conductor from either of said sources of electromotive force being ineffective to operate said second differential relay and the change in the energization of said one winding of said second differential relay responsive to the Iclosure of a 10W resistance signaling circuit over said other conductor from either one of said sources of electromotive force being effective to operate said second differential relay.

11,'In a signaling system according to claim. l0, relays selectively controlled by said first and second polarized relays and said first differential relay, relays selectively controlled by said third and fourth polarized relays and said second differential relay, and means selectively controlled by said relays to indicate the digits corresponding to the operated keys of said signal transmitting means.

12. In a signaling system, a signaling conductor, signal relays connected to said conductor for selective response to marginal and polarized direct current signals, and monitoring means connected to said conductor for response to said signalsQsaid monitoringk means comprising two thermionic direct-current amplifiers, relay means selectively controlled by one of said amplifiers for indicating the polarity of a signal transmitted over said conductor, relay means controlled by the other of said amplifiers for response only to signals of maximum amplitude transmitted over said conductor, means comprising a high resistance element operatively connecting the cathodegrid circuits of said ampliflers to said conductor, and a condenser connected to said element in parallel With the cathode-grid circuits of said amplifiers to prevent the operation of said relay means responsive to transient voltages impressed on said conductor.

HENRY E. VAUGHAN. 

